1. Field of the Invention
The present disclosure relates to transfer of a user equipment from a cell to another in a communications system.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, data, multimedia and so on. A user equipment connected to a communication system may, for example, be provided with a two-way telephone call or multi-way conference call or with a data connection. In addition voice call services, various other services, for example multimedia services or other data services, may be provided for a user. A user equipment may communicate packet data to and from a server entity, or between two or more user equipments.
A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standard or specification may define if a user equipment is provided with a circuit switched service or a packet switched service or both. Communication protocols and/or parameters which shall be used for the connection are also typically defined. For example, the manner how the user equipment can access the communication system and how communication shall be implemented between the user equipment and the elements of the communication network is typically based on predefined communication protocols. In other words, a specific set of “rules” on which the communication can be based on needs to be defined to enable the user equipment to communicate via the communication system.
Communication systems proving wireless communication for user equipment are known. These systems are commonly referred to as mobile systems, although in certain systems the mobility may be restricted to substantially small areas. An example of the mobile systems is the public land mobile network (PLMN). Another example is a mobile system that is based, at least partially, on use of communication satellites. Mobile communications may also be provided by means of other types of systems, such as by means of wireless local area networks (WLAN).
In a typical mobile system the user equipment may communicate via a station of the communications, commonly referred to as a base station. A station provides user equipment with an access to the communication system. This access area provided by a base station is commonly referred to as a cell. A user equipment may be in wireless communication with two or more base stations at the same time. A user equipment may also be configured to communicate with base stations of different communication networks, i.e. are adapted for operation in multi-radio environments. Communication on the wireless interface between the user equipment and the base station(s) can be based on appropriate communication protocols.
The operation of the apparatus of an network is controlled by an appropriate control arrangement commonly including a number of various control entities with different functions. Control of the access network side (i.e. the cells) and the core network side of a network is typically separated.
Mobile users are provided with various services. The availability and use of different services is also believed to increase as the networks are improved to provide more data carrying capacity and features enabling service providers to offer even more sophisticated services.
An example of the services are the so called real-time services, for example video or audio or other services wherein data streaming is provided. Real-time services are expected to be increasingly popular amongst the users of mobile user equipment. Real-time service such as video streaming can be a high bitrate service that requires certain capability in the mobile user equipment and the network for enabling sufficiently high bitrates, which is generally more critical in the uplink from the user equipment to the base station. This data rate requirement is met based on different protocols and mechanisms in different networks. For example, the second generation (2G) GSM access systems can be upgraded by enhanced general packet radio service (EGPRS) capability to better meet the requirements for data streaming and so-called conversational traffic classes that have even tighter delay requirements than streaming services. Another option for enhancing the 2G is the dual-transfer mode (DTM) which provides a parallel 2G circuit switched and packet switched (CS, PS) service. The third generation (3G) systems, on the other hand, are commonly provided from the outset with a bitrate capacity that enables data streaming.
In order to make the introduction of the real-time services a success the services should work smoothly also in multi-radio environments, for example in environments wherein the data bearer may be provided by the 3G wideband code division multiple access (WCDMA) or 2G GSM. A critical point in providing the service is when there is a need to change the system, for example to transfer user equipment from a 3G WCDMA network to a 2G GSM network. This situation may occur for example when the mobile user equipment leaves a WCDMA cell or otherwise needs to be handed over from a 3G cell to a cell of another network.
Due to existing mechanisms such as routing area updates (RAU) and other factors the interruption time during which no user data can be transmitted is currently in the order of several seconds. Buffering of streaming data can to some extend bridge the interruption time. Buffering, however, may not be an appropriate long term solution, especially because the experienced interruption may be too much and as said conversational traffic has tighter delay requirements. Also, as the number of users increases the requirement for buffering capacity increases accordingly, and the buffering may not always be practical. A solution for the problem of providing a smooth service performance during a system change would also be beneficial because conversational services, i.e. voice calls, do not allow buffering.
Due to needed new hardware and associated cost when upgrading 2G GSM cells to EGPRS, some cells may remain GPRS-only enabled, either for quite some time or even for the remaining lifetime thereof. However, the radio network controller of the 3G cell is not by default aware about the neighboring 2G GSM cell capabilities. These capabilities may include capabilities such as the above referenced Enhanced GPRS (EGPRS) and dual-transfer mode (DTM), and so forth.
Therefore the radio network controller of the 3G cell may not be capable of ensuring that an handover of an EGPRS capable mobile user equipment or similar will occur directly to an appropriate, and preferably to the most suitable cell for the user equipment, for example to an EGPRS capable cell. If the mobile user equipment is handed over to a GPRS-only cell, it will need a new cell re-selection or handover procedure from the non-enabled cell to an EGPRS enabled cell. This increases the unwanted service interruption times significantly. The quality of real-time services like video streaming would suffer, especially if the GPRS cell cannot provide the required bitrate.
It is noted that the problem is not limited to mobile systems, but may occur in any communication environment wherein user equipment may nerd to be transferred to an access system of a different communications system.